1. Field of Invention
The present invention relates to a filament lamp, particularly to a filament lamp for heating an object to be treated.
2. Description of Related Art
The production steps for solar cells include a thermal diffusion step for diffusing a P type semiconductor and a baking step for baking silver paste to make electrode material. In both steps, a semiconductor wafer and a glass substrate are heated to a high temperature of around 800° C. to 900° C. using a thermal diffusion furnace and a baking furnace, respectively.
In such a heating device, an object to be treated must be heated uniformly in order to avoid a locational variation of temperature. For this reason, what has been proposed is a structure capable of providing multiple power supply pathways inside the luminous tube of a filament lamp as a light source and independently supplying a desired amount of electricity to each pathway (Japanese Laid-open Application No. 2006-279008 and corresponding U.S. Patent Application Publication 2006/0197454). However, the temperature to which an object to be treated is heated in the production steps noted above has been increasing, and the amount of electricity to be supplied to a lamp has also been increasing. On the other hand, the size of a lamp cannot be increased, and there is a demand for reducing the size thereof instead.
Each filament is connected with an internal lead for supplying electricity, and internal leads form complicated pathways inside a luminous tube. For this reason, there occurs a problem that an internal lead and a filament or two internal leads electrically short to each other or that a filament comes off a specified position. In other words, in a filament lamp having a plurality of independent power supply pathways, the lamp has an extremely complicated structure so that an object to be treated can be heated uniformly. As a result, the abovementioned problems occur.